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Thin provisioning and virtual disks
52 Dell EMC SC Series: Best Practices with VMware vSphere | 2060-M-BP-V
12.1.3 Thin provisioned (thin)
The logical space required for the virtual disk is not allocated during creation, but it is allocated on demand
during the first write issued to the block. Like thick disks, this format will also zero out the block before writing
data, inducing extra I/O, and an additional amount of write latency.
12.1.4 Space efficient sparse (SE sparse disks)
SE sparse disks are a new virtual disk type introduced for use with VMware Horizon View Composer. These
virtual disks are used with linked clones for improved performance, space reclamation, and a new 4 KB grain
size.
12.2 Thin provisioning relationship
The following points describe how each virtual disk format affects SC Series thin provisioning:
• Thick provision lazy zeroed: SC Series thin provisions the virtual disks.
• Thick provision eager zeroed: SC Series thin provisions the virtual disks (see section 12.3).
• Thin provisioned: SC Series thin provisions the virtual disks. There are no additional storage savings
while using this format because the array already uses its thin provisioning (see section 12.4).
• SE sparse (available with VMware Horizon View virtual desktops): SC Series thin provisions the
virtual disks. Space reclamation within the VMDK is available.
As a best practice, use the default virtual disk format of thick provision lazy zeroed unless there are specific
needs to pre-allocate virtual disk storage. Needs such as Microsoft clustering, VMware Fault Tolerance (FT),
or for virtual machines potentially impacted by the thin or zeroedthick on-first-write penalties. If the application
is sensitive to VMFS write penalties, it is recommended to test eagerzeroedthick virtual disks to determine the
performance impact.
12.3 SC Series thin write functionality
Most versions of SCOS can detect incoming sequential zeroes while being written and track them, but not
write the zeroed page to the drives. When creating virtual disks on these versions of firmware, all virtual disk
formats will be thin provisioned at the array level, including thick provision eager zeroed.
12.4 SC Series thin provisioning or VMware thin provisioning
A common question is whether to use array-based thin provisioning or the VMware thin provisioned VMDK
format. Since SC Series uses thin provisioning on all volumes by default, it is not necessary to use VMware
thin provisioning because there are no additional storage savings by doing so.
However, if VMware thin provisioning is needed, pay careful attention not to accidentally overrun the storage
allocated. To prevent any unfavorable situations, the integrated vSphere datastore threshold alerting
capabilities should be used to warn against running out of space on a datastore. The threshold alerting
capabilities of Dell Storage Manager can also be used to alert for low-space conditions.
12.5 Windows free space recovery
Windows NTFS file system with Windows Server
®
2012 and prior has a reporting nuance. Over time, the
usage of the file system can grow apart from what the array reports as being allocated. In this example, there
is a 20 GB data volume where Windows writes 15 GB worth of files, followed by deleting 10 GB worth of